This invention relates to a one-way clutch which either produces or refrains from producing a rotational output, depending on the direction of the rotational input. More particularly, the present invention relates to a one-way clutch which is effectively utilized as one element of a damper device capable of absorbing the shocks of an opening or closing motion of a lid in a cassette tape recorder or video tape recorder and which generates a shock-absorbing function while the lid is being opened and remains inactive while the lid is being closed.
Various types of one-way clutches have been heretofore proposed, including spring type, ratchet type, free wheel type, and planet type clutches.
The spring type clutch is formed by encasing a coil spring in a cylinder on the driving shaft side or the driven shaft side in such a manner that the driven shaft or driving shaft will come into sliding contact with the inside boundary of the coil spring. In this spring type clutch, the driving shaft produces idle rotation while the clutch is rotated in one direction relative to the direction of the winding of the coil spring and the coil spring contracts or expands radially to effect transfer of motion from the driving shaft to the driven shaft while the clutch is rotated in the other direction. This spring type clutch has the disadvantage that the transfer loss is increased and the durability is decreased in proportion as the load on the driven shaft side increases.
The ratchet type clutch comprises a ratchet pawl and a ratchet wheel. This ratchet type clutch provides efficient transfer of rotation in one direction but produces a clicking noise while it is producing idle rotation in the other direction.
The free wheel type clutch has a roller encased in a wedge-shaped empty space formed between a driving shaft and a driven shaft and effects transfer of motion by virtue of the friction arising from the wedge effect. When the rotation is reversed from the idle rotation, the transfer of motion is delayed by the time which is spent by the roller during its motion through the wedge-shaped empty space. The free wheel type clutch suffers not merely from this slow response but also from a loss of motion by slippage which is too large to be ignored.
The planet gear type one-way clutch comprises an inner toothed ring having inner teeth on a cylindrical wall, a panel fitted to the inner wall of the inner toothed ring and adapted to be rotated relative to the aforementioned inner wall of the inner toothed ring, and a shaft pivotally attached to the aforementioned panel, so that during the rotation of the inner toothed ring in one direction, the shaft will be meshed with the inner teeth to set the panel rotating in concert with the inner toothed ring and induce rotation of the shaft fixed to the panel and, during the rotation of the inner toothed ring in the other direction, the shaft will break engagement with the inner teeth to leave only the inner toothed ring in idle rotation. As compared with the conventional type which constantly maintains a ratchet pawl drawn with a spring and meshed with the ratchet inner teeth of an inner toothed ring, this planet gear type clutch has a unique effect in that it eliminates the clicking noise otherwise generated during idle rotation of the inner toothed ring. It nevertheless has the disadvantage that the construction thereof is somewhat complicated and the number of component parts used therein is quite large.
It is conceivable to use any of the clutches described above in a shock-absorbing device in a mechanism for opening and closing a lid in various types of machines to fulfill the purpose of producing an amply braked opening motion while the lid is being opened and releasing the braking force while the lid is being closed thereby protecting the machine against the shocks of the opening and closing motions of the lid and, at the same time, ensuring smooth opening and closing motions. The conventional dampers usable in applications of this nature come in various types including the oil type and the air type, for example. To be more specific, when a rotary damper is incorporated as in a mechanism for opening and closing a lid-like cassette holder case in a video tape recorder or a mechanism for opening and closing a lid of an instrument in an automobile for the purpose of absorbing abrupt motion of the lid while the lid is being moved by a spring from its closed state, the rotary damper is similarly actuated when the lid in open state is closed by a push with the hand. Thus, the lid is hindered from being lightly closed. In this case, the difficulty might be removed by incorporating a one-way clutch in addition to the rotary damper so that while the lid is being closed, the one-way clutch prevents the motion of the lid from being transferred to the rotary damper and the rotary damper is actuated only when the lid is opened from its closed state. To permit this additional incorporation of the one-way clutch, however, it would be necessary for the separately produced rotary damper and one-way clutch to be joined with the former's output shaft connected to the latter's input shaft and, in the joined state, incorporated into the mechanism. Thus, the mechanism incorporating them both would become quite bulky.